A mobile service provider typically provides wireless coverage in a designated geographical area, such as a particular country or one or more Metropolitan Service Area (MSA). When the service provider's subscribers require mobile service within these areas, the subscribers' mobile phone or user equipment searches for and attaches to the service provider's network. When a subscriber travels outside the service provider's designated coverage area, the subscriber's mobile phone is considered to be roaming and must attach to another service provider's mobile network—a visited network—to obtain service. The visited network exchanges information with the home network when the subscriber attaches to verify that the subscriber's mobile phone is a valid device. If an authentication message exchange is successful, the roaming subscriber obtains service from the visited network.
For example, a subscriber of a U.S.-based mobile network may travel to Europe. To obtain mobile service while in Europe, the U.S.-based subscriber's mobile phone must look for and attempt to attach to a European service provider's mobile network. The roaming mobile device may detect multiple potential visited networks. Typically, the mobile device will attach to the visited network having the strongest signal.
Often, a home mobile service provider will enter into contractual agreements with preferred foreign service providers that provide coverage in areas outside the home service area. Such contracts may provide, for example, lower billing rates and/or a guaranteed class of service for roaming subscribers from the home network. Accordingly, the home network service provider usually wants its subscribers' roaming mobile devices attach to a preferred foreign service provider. To accomplish this, the home network uses Steering of Roaming (SoR) in an attempt to guide its subscribers' mobile devices to the preferred visited networks. In order to maintain the roaming subscriber on its network, or to prevent the roaming subscriber's from using another visited network, some non-preferred visited networks employ Anti-Steering of Roaming (Anti-SoR) techniques.